Some people here are saying that you need to focues, wich I agree with. But I know students don't work 100% of the time in class. Some people finish early and you have nothing to do but go on facebook and wait for the bell.
I remember when I went to high school I would just type in facebook.com then a page would come up saying its blocked and will say a website. Just keep clicking the websit until it shows up. But beware that it may take a long time for it to show up.
Heaven forbid you actually focus on schoolwork at school. Get on Facebook when you get home. Your attempts to get on Facebook can be logged, and will probably result in a revocation of your computer privileges.
You should have no need for social media at school. They have it blocked for a reason, live with it! Not being rude, I can understand the need for people to have a social life, but there are a few places where your concentration should be on more important things.